Interference and enhancement effects on interaural time discrimination and level discrimination in listeners with normal hearing and those with hearing loss

It is known that many listeners with sensorineural hearing loss (SNHL) have difficulty performing binaural tasks. In this study, interference and enhancement effects on interaural time discrimination and level discrimination were investigated in 4 listeners with normal hearing (NH) and 7 listeners with SNHL. Just-noticeable differences were measured using 1/3-octave narrowband noises centered at 0.5 and 4 kHz. Noises were presented in isolation and together at equivalent sound pressure level (EqSPL) and equivalent sensation level (EqSL). Each noise served as target and distractor in the dual-band conditions. Congruent conditions included interaural differences in both noises that varied together, and incongruent conditions included an interaural difference in one noise with the second noise diotic. No significant enhancement effects were observed for either group in either task. Interference effects for the NH group were limited to the interaural level discrimination task in the 0.5-kHz target and 4-kHz distractor condition. Performance of participants with SNHL was similar to that of the NH group for interaural time discrimination with noises at EqSL but not EqSPL. In interaural level discrimination, listeners with SNHL demonstrated interference with a 4-kHz target and 0.5-kHz distractor. Results indicated that the relative levels of low-and high-frequency targets and distractors could affect binaural performance of individuals with SNHL but that in some conditions listeners with SNHL performed similarly to those with normal hearing. Implications of these results for binaural clinical tests and hearing aid fitting strategies are discussed.